The invention relates to a process for producing a refractory lining of a ladle or metallurgical vessel for casting steel. The refractory lining also serves as the inner (wear) lining for the ladle or metallurgical vessel. The inner lining is produced by using a thixotropic vibrational lining mass. The lining incorporates wall passages with conical nozzle bricks and/or bubble bricks. Each of the bricks is mortared into an opening without using seating blocks. The bricks are mortared into the openings so that the bricks remain free from contact with the inner lining.
The fundamentals of such a process form part of the state of the art, owing to a paper read by T. Mafune and M. Chastant on Oct. 29 and 30, 1985, in Nancy at the meeting "Journees d'Information Techniques de Mise en Oeuvre des Produits & Materiaux Refractaires [Technical Information Days about the Use of Refractory Products and Materials]". It is also discussed in DE-C-3,741,073. The difference between this type of lining and the conventional brick-lining with refractory bricks is that the lining is formed as a monolithic block. The lining is produced in such a way that a template defining the clear opening of the ladle is lowered into the latter and the interspace between the inner ladle wall and the template is filled with a thixotropic refractory mass which, under the action of vibrators, flows readily and is compacted. If the lining is worn after a number of ladle campaigns, repair can be effected in a relatively simple manner by applying new thixotropic refractory mass with the aid of the template, after the surface layer of the old lining has been removed, as described in DE-C-3,741,073.
The aims are to extend the service life of such a lining for as long as possible without repairs which interrupt the sequence of operation. In fact, the ladles and the metallurgical processes to be carried out in them have gained increasing importance in modern metallurgy. In particular, the so-called ladle furnace now plays a decisive part in steel production. The ladle is equipped with bottom bubble bricks and a cover with three arc electrodes for heating and bubbling gas through the molten steel. The electric arc furnace and the oxygen top-blowing converter have become simply melting-down units. In the ladle furnace, however, the steel is adjusted, alloyed, correction-alloyed and brought to an exact temperature, so that the important cost-saving sequential cast in continuous casting can be ensured. The ladle furnace is thus an important vessel in modern steel production and must be absolutely reliable and safe. Every melt exerts an erosive attack on the lining. A particular problem is represented here by the perforated bricks and bubble bricks, i.e. the bricks in the region of the tapping hole and in the region of the points where gases are blown from the outside into the molten steel in the ladle.
The hitherto usual technique at such wall passages of the ladle is to insert the actual nozzle bricks, i.e. bush-like elements of particularly high-grade refractory material, and bubble bricks, i.e. porous bricks of in most cases conical shape for blowing in gaseous media, into special seating bricks, i.e. bricks which are in turn seated in the lining and receive the nozzle bricks or bubble bricks in a central perforation. "nozzle bricks and/or bubble bricks" are thus meant to be the actual functional bricks which come into contact with the melt running out and/or with the gas blown in, and "seating bricks" are meant to be separate bricks which are inserted into the surrounding lining and form the fixing for the abovementioned bricks. For the nozzle brick of the tapping hole or spout this technique is evident from Stahleisen-Schrift, Issue No. 8 "Das StranggieBen von Stahl [Continuous Casting of Steel]", published by Stahleisen GmbH (Dusseldorf 1975), page 58, and for bubble bricks from GB-A-2,122,532. The seating bricks were, in conventional brick-lining, a constituent of the refractory masonry and are inserted, during the production of the lining from vibrational masses, into openings thereof kept free by means of templates.
Under the erosive action of the melt, these seating bricks wear out in most cases at increasing rates. In such a case, the ladle had hitherto to be cooled, so that the bricks could be broken out and replaced by new ones. Troublesome interruptions in operation were the consequence.
The technique of inserting the actual nozzle bricks and/or bubble bricks into separate seating bricks has always been retained, in spite of the associated inconveniences due to the wear of the seating bricks. This also applies to-the time after the development of the monolithic linings. The bricks were present, unchanged, even in rectangular shape, which is a relic from the period of bricked linings.
This also applies to the teaching according to DE-B-2,233,894, which relates to the lining of a metal-lurgical vessel with a lining mass which can be made to flow by vibration but is not thixotropic. The runner brick, which can be vibrated into the lining mass or can be inserted later, after the introduction of the mass, into a region kept free at that time, is drawn diagrammatically as a unitary body, but it consisted in fact of a seating brick and nozzle brick in accordance with the then current technique.
The blowing brick according to DE-C2-3,433,123 is cased in its lower region with a metal sheet and, in its upper region, directly adjoins the lining of the ladle and, after the ladle has been put into operation, its surface sinters together with the lining, whose type is not described. It forms a unit with the lining and cannot be replaced without major breaking-out work.
The literature reference "Bottom inert gas blowing into an electric arc furnace at Vallourec" in "Metallurgical Plant and Technology International", 6 (1990), pages 54-61, discloses an electric arc furnace, in which a blowing brick of MgO is tamped directly into an MgO lining and bonds with the latter under the action of the melt to form a unit.
A replacement of the bricks in the abovementioned embodiments is made-particularly difficult by their cylindrical shape in the region adjacent to the lining, which shape makes it virtually impossible, in conjunction with the direct sintering together with the surrounding lining, to eject the brick residues.